This invention relates to water softening apparatus, and more particularly to an improved automatic control for the regeneration of a water softener tank.
Several different approaches to the control of the regeneration of a water softener resin bed are in use. They vary in sophistication from a simple manual control in which the user manipulates valves to accomplish the steps necessary for withdrawing the resin bed from service connecting the bed first to a source of regenerative fluids and then to a source of rinse water, and then returning the bed to service. A more automatic control will typically include a timer which triggers the automatic manipulation of valves for the regeneration cycle at a particular day of the week and time of day. The most sophisticated are controls which sense the condition of the water being treated and initiate regeneration when the quality of the water indicates that the resin bed is becoming exhausted. The present invention has to do with these automatic sensing type of water softener control.
An example of an automatic sensing water softener control is found in U.S. Pat. No. 3,574,330 issued Apr. 13, 1971 to David G. Prosser and assigned to the assignee of this application. That sensor control combines a sensing mechanism which detects the exhaustion of the resin bed and a timer which provides a drive through a multiport valve that causes the proper hydraulic circuit changes to accomplish regeneration of the resin bed. The sensing mechanism consists of a small volume of ion exchange resin held in a cell separate from the resin bed, a mechanism to detect the change of the cell resin which will occur between the conditions when the cell resin is regenerated and when it is exhausted, and a linkage to cause the timer to start a regeneration sequence. The timer also has the function of operating a small valve every twenty-four hours to allow a flow of water through the cell resin. This flow of water originates from a probe located in the softener resin bed and flows through the sensor cell to drain. Since the water being withdrawn from the resin bed of the softener has already passed through a major portion of that bed, it should be softened so that it has no effect on the cell resin. If the resin bed is exhausted to the level of the probe, the water withdrawn will cause the cell resin to change volume. In the specific commercial implementation the resin shrinks and this shrinkage is detected by the output mechanism which then causes the timer to start a regeneration sequence of valve shiftings.
During the subsequent regeneration of the softening resin bed the sensing cell resin must also be regenerated so as to return it to its initial volume. This has been accomplished by opening the valve between the probe and the sensing cell during the brine and rinse period of the regeneration sequence. With this valve open, brine in the softening resin bed flows through the cell thereby regenerating the cell resin. Rinse water which has passed through the softening resin bed will also pass through the cell resin.
The foregoing arrangement for regenerating the cell resin may not produce the desired results. This appears to be caused by two factors. First, the brine which enters the probe inlet on its way to the cell resin has already passed through a major portion of the softening resin bed. In doing so there will have been an exchange of calcium and magnesium ions with the sodium ions. As a result the brine that enters the probe inlet can contain a high relative proportion of calcium and magnesium ions to sodium ions and there is an insufficient supply of sodium ions to make the necessary ion exchange in the cell resin. Since the cell resin is not fully regenerated, when next tested by the timer, it would not have returned to its full volume and can therefore give a false signal that regeneration is required. This results in unnecessary regeneration of the softener resin bed.
Secondly, concentrated ions are found in the regeneration effluent after the typical sodium chloride brine has passed through a large portion of the softener resin bed. These concentrated ions include iron and they tend to adversely effect the cell resin. One adverse result suspected is a condition known as "packy" resin in which the resin loses its fluidity so that it will not flow when the plunger which is part of the output mechanism is brought to bear against the cell resin. This can produce a faulty signal. The problem is more acute with the special resins which are used in the sensing cell since they are selected to exhibit a greater volume change between regenerated and exhausted conditions.
The present invention provides an apparatus and method for alleviating the foregoing problems and for insuring that the cell resin is always in a condition to properly sense the need for regeneration of the softening resin bed.